Experimental results are presented for the phase split which occurs at a T-junction made up of 0.125 m diameter pipes all on the same horizontal plane. Measurements were performed in the stratified and annular flow regimes and near the boundary of stratified-annular flow. A new phenomenological model is presented to determine the phase split of low liquid hold-up (<0.04) semi-annular flow and predictions compared with measurements from this present study, other sources of data and published phase separation models. Excellent agreement is found dependent upon the various correlations implemented in the model.